1. Field of the Invention
This invention relates to an improved fluid sample cell for the spectroscopic analysis of a fluid sample.
2. Description of the Prior Art
A number of fluid sample cells are known in the art for the containment of fluid samples during transmission spectroscopic analysis. These cells typically include one opening for the entrance and one opening for the exit of radiant energy, and are positioned in a spectroscopic instrument where a contained sample is irradiated with radiant energy. After passing through the sample, the radiant energy is detected and analyzed to determine the absorptive characteristics of the sample or a constituent thereof.
Because the sample cells of the prior art typically provide the opening for the entry of radiant energy on one side of the cell and the opening for the exit of radiant energy on the other side, the instruments of the prior art usually comprise a radiant energy generating means disposed above the sample cell and a radiant energy detector disposed below the cell. Thus, the length of the instrument must be at least as long as the distance between the generating means and the cell plus the distance between the cell and the detector. This required length of conventional instruments causes them to be bulky and inconvenient.
A spectroscopic instrument that does not necessarily involve the length of other more conventional prior art devices is described in U.S. Pat. No. 4,278,887. There, a fluid sample cell is provided which defines a sample compartment having a radiation energy transmissive top and a bottom composed of a diffuse reflector, such as a diffuse mirror. In operation, a sample in the compartment is irradiated with radiant energy and the radiant energy is diffusely reflected back through the transmissive top to detectors which are located on the same side of the cell as the radiant energy generator.
However a problem with the fluid sample cell described in U.S. Pat. No. 4,278,887 is the relatively low amount of radiant energy that is transmitted to the radiant energy detectors. Because the bottom of the cell consists of a diffuse reflecting surface, radiant energy impinging upon the surface may be reflected at any reflective angle and only a fraction of the radiation traveling in a straight line from the radiation source will arrive at the radiation detector. The relatively low transfer of radiant energy to the detector can compromise the accuracy of the spectroscopic analysis.
Accordingly, there exists a need in the art for a fluid sample cell for use in transmission spectroscopic analysis which is compact and convenient to use, and which will help to avoid inaccuracies of measurement due to inadequate radiant energy transmission to radiation detectors. The present invention satisfies these needs, and fulfills other objectives which will become apparent from the following.